Various types of positioning systems for determining a position based on radio signals are known in the art. For example, satellite navigation systems allow autonomous geospatial positioning with virtually global coverage. Global navigation satellite systems (GNSS) provide GNSS receivers with the capability to determine their location based on positioning signals transmitted from the GNSS satellites in terms of longitude, latitude and altitude, to within a few meters or even centimeters.
A GNSS makes use of a constellation of satellites orbiting the earth to provide signals to a receiver that estimates its position relative to the earth from those signals. Examples of such satellite systems are the NAVSTAR Global Positioning System (GPS) deployed and maintained by the United States, the GLObal NAvigation Satellite System (GLONASS) deployed by the Soviet Union and maintained by the Russian Federation, and the GALILEO system currently being deployed by the European Union (EU). Additional systems such as Galileo (European Union) and Compass (China) are planned. A GNSS receiver typically utilizes signals from satellites of one or more of such Global Navigation Satellite Systems.
The civilian uses of GNSS receivers for surveying, positioning, navigation, tracking, timing, and many other uses has become very widespread. Unfortunately, the nature of the GNSS signals and GNSS receivers (at least from a civilian perspective) is that they are very weak and are easily susceptible to jamming, spoofing (e.g., providing false signals or information to impede determining a position fix), interference, and other disruption (malicious or unintended) which can easily compromise the integrity of the signals reaching a GNSS receiver or the positioning output generated by a GNSS receiver. In a world of increasingly crowded broadcast frequency spectrum and increasingly sophisticated and ambitious hackers, such compromises to the integrity of GNSS signals are very likely to increase. This may lead to GNSS receivers failing to track satellites, or in the case of spoofing or weak jamming may lead to GNSS receivers providing incorrect positioning output.
Typically, a high powered jammer, spoofer or the like would quickly be noticed and discovered. However, due to the very weak nature of GNSS signals arriving at or near earth level from space, a low-powered jammer, spoofer, or the like (malicious or otherwise), may be very localized and hard to detect and/or locate. This can be a particularly insidious problem if the localized region affects a GNSS reference station that broadcasts corrections for use by GNSS receivers in a wider geographic region that surrounds the reference station. This is because such reference stations are often utilized for precise navigation of ships near harbors, precise navigation of aircraft, or precise survey work. Thus, a disruption to the integrity of GNSS signals received by a GNSS reference station may lead to many catastrophic or disruptive problems such as, but not limited to: ships running aground, aircraft crashing, and construction crews being unable to perform work, or performing their work incorrectly in the case of spoofing.